Natural martite microparticles (NMMs) were prepared with a high energy planetary ball mill to form a nanocatalyst for a Fenton-like process. Martite nanoparticles (MNs) of different scales are formed when the milling time ranges from 1 to 5 h at the milling speed of 300 rpm. The catalytic performances of MNs are higher than the NMMs for the degradation of acid blue 5 (AB5) in a heterogeneous Fenton- like process. The NMMs and the MNs were characterized by SEM, EDX, BET, XRD and FT-IR analyses. The size distribution of the 5 h milled martite nanoparticles (MN3) is in the range of 20 nm to 100 nm, and these have the highest surface area (19.23 m(2) g(-1)). The influence of the main operational parameters, including initial pH, MN3 dosage, H2O2 and initial dye concentration, were investigated on the AB5 degradation. The treatment process obeys pseudo first order kinetics and some of the degradation intermediates were recognized by the GC-MS method. The environmentally-friendly production of the MNs, low amount of leached iron and repeated catalyst usage are the significant advantages of this research. Finally, an artificial neural network (ANN) is expanded to estimate the degradation efficiency of AB5 on the basis of the experimental results, which indicates the appropriate performance (R-2 = 0.955).